Ferrous alloy



Patented May 1, 1934 FERROUS ALLOY Frederick C. Langenberg, Edgewater Park, N. 1., assignor, by direct and mesne assignments, of one-half to United States Pipe & Foundry Company, Burlington, N. J., a corporation of New Jersey, and one-half to Crucible Steel Company of America, a corporation of New Jersey No Drawing. Application January 19, 1931, Serial No. 509,887

.4 Claims.

My invention relates to the composition of forgeable ferrous alloys incorporating chromium and characterized by corrosion resisting qualities, such alloys boing commonly designated stainless steels and irons. It is well known that alloys of this character are not free cutting and for this reason possess undesirable qualities, especially in being difiicult to machine and the object of my invention is to so compound a ferrous alloy of the class indicated as to impart to it free cutting qualities without detracting from its corrosion resisting or stainless characteristic and without bringing about the quality known as red shortness or other undesirable qualities and my invention depends upon my discovery that the incorporation in a forgeable corrosion resisting alloy of the class described and of any otherwise usual composition of diffused fine particles of molybdenum sulphide will impart to the alloy free cutting qualities without detraction from its corrosion resisting qualities and without bringing about red shortness or other detrimental qualities.

The compositionof my alloy as determined by analysis will difier from that of usual stainless forgeable alloys containing chromium in. that my alloy will contain sulphur in excess of such percentage as will unite with any manganese which may be present in the alloy and molybdenum in at least sufiicient percentage to provide for its combination with the excess sulphur and the consequent formation of molybdenum sulphide but it must be understood that the sulphur constituent of my alloy in excess of that combined with the manganese constituent must-be substantially all combined with the molybdenum constituent and therefore present in the form of molybdenum sulphide, the presence of which in the form of distributed particles throughout the whole renders the alloy free cutting without imparting to it the quality of red shortness and without impairing its corrosion resisting qualities, the molybdenum sulphide being in itself highly corrosion resistant and it being also true that its presence in the alloy does not otherwise impair its corrosion resisting quality. The percentage of molybdenum sulphide may vary within wide limits, and will be regulated somewhat upon the toughness which would characterize the alloy in its absence and somewhat on the degree to which it is desired that the quality of free cutting should be imparted to the alloy. v

In practice I have compounded my alloy with sulphur present in from .08 to '.25% and with molybdenum in all cases in suflicient percentage to provide for its combination with all sulphur in excess of that combined with the manganese element if present in the alloy. I have found it convenient to use molybdenum in my alloy in percentage from .25 to .50, and I would state that in all cases I prefer to keep the manganese as low as compatible with good mill practice because while the presence of manganese sulphide in the I alloy does not impair the free cutting quality im parted to it by the molybdenum sulphide, it does 55 to a certain extent impair the corrosion resisting properties of the alloy.

As a typical example of the analytical composition of an alloy embodying my invention, I will give the following:

Carbon Manganese Phosphorus Sulphur Sulphur; Silicon .18 Nickel .06 Chromium 12.73

Molybdenum .31

It must be borne in mind however that in my alloy the sulphur must not be present in the form of eutectic forming sulphides which would bring about the quality of red shortness and must be to a large extent present in the form of molybdenum sulphide though in alloys comprising manganese, sulphur may also be present in the form of manganese sulphide without impairment of the free cutting characteristic of my alloy. It will be recognized by those skilled in the art that in the absence of the molybdenum sulphide component steel having the composition indicated by the analysis would be either very tough and difficult to machine if sulphur was only present to the extent usually considered permissible or would, if the sulphur was present in higher quantity and uncombined with molybdenum, be characterized .120 gravimetric .040 volumetric I by red shortness.

constituent of the alloy it is desirable that this substance should be formed in situ and this I accomplish by incorporating in a melted bath of the ferrous alloy, chromium in sufllcient percentage to impart to the alloy corrosion resisting qualities, in common practice not less than 8%, sulphur in excess of the percentage which will combine with any manganese present in the alloy and molybdenum in sufiicient quantity to combine with the excess sulphur, with formation of molybdenum sulphide, as a result of which molybdenum sulphide is formed as precipitated particles uniformly dispersed and having the small particle size characteristic of precipitates. The combining ratio of molybdenum and sulphur is of course well known but as molybdenum in moderate percentage is not considered a detrimental component of ferrousalloys of the class had in view, it will obviously be desirable to add molybdenum in somewhat greater quantity than that indicated by this combining ratio with sulphur so as to insure that substantially all the sulphur not combined with manganese will be converted into molybdenum sulphide.

It is obviously necessary to bring about the difiusion of the particles of molybdenum sulphide throughout the alloy, that both the sulphur and molybdenum should be generally and in effect evenly distributed throughout the melted alloy; There is no difiiculty in effecting the necessary dispersion of the sulphur in the melted bath but to obtain a similar dispersion of the molybdenum in the bath it is practically necessary that the molybdenum should be added in some non-volatile form and this can readily be eifected by adding molybdenum in the form of term molybdenum, which will readily diffuse itself throughout the melted bath or the same result can be obtained by adding the molybdenum in the form of a non-volatile salt, of which-the most available is calcium molybdate. Such salts are decomposed by the heat of the bath, permitting their molybdenum content to readily diffuse itself through the bath.

My method of compounding the alloy is applicable in connection with any of the usual stainless alloys.

It will be understood by those skilled in the art that my improved stainless steel comprises only that class of stainless steels which derive their stainless or corrosion resisting qualities from the incorporation in the alloy of chromium in sufficient percentage to impart to the alloy corrosion resisting qualities to the extent which will impart to the alloy the quality generally referred to as stainlessness. Such steels contain not less than 7% of chromium and for practical purposesmay be said to contain not more than 35% of chromium. In other respects, my improved alloy may be compounded with any of the constituent elements used in the compounding of stainless steels adapted for use for difierent purposes, such, for example, as are described in Steel and its Heat Treatment by D. K. Bullens, third edition, published in New York, 1927, chapter on stainless steels, pp. 280 to 292, the essential novel feature of my stainless steel being that it incorporates sulphur in excess of such amount as would combine with the manganese present in the alloy, molybdenum in sufficient quantity to combine with such excess sulphur and that the excess sulphur is distributed throughout the alloy in the form of precipitated particles of molybdenum sulphide.

It is well known that stainless steels not infrequently incorporate certain generally minor percentages of other ingredients than chromium, manganese and sulphur, such, for example, as tungsten, copper, vanadium, cobalt, silicon, nickel and zirconium, and it will be understood that I do not intend to exclude such possible alloying elements from the scope of my claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. A corrosion resistant, forgeable, alloy steel comprising chromium in excess of 7% and not to exceed 35%, characterized in that it embodies sulphur in excess of such quantity as will combine with the manganese constituent of the alloy, said sulphur being present in percentage between .07 and 2%, and molybdenum in excess of such quantity as will reactively combine with the excess sulphur and in percentage between .10 and 5%, and in that the excess sulphur is substantially all present in the alloy in the form 115 of distributed particles of molybdenum sulphide having the fine particle size characteristic of precipitates, the balance of said alloy being substantially iron.

2. An alloy as called for in claim 1, embody 120 sulphur in percentage between .08 and .25.

' 3. An alloy as called for in claim 1, containing sulphur in percentage of approximately .120 and molybdenum in percentage of approximately .31.

4. A stainless steel containing a chromium 125 content of about 13%, molybdenum from about .3% to about 45%, sulphur from about .l% to about 25%, and characterized by having free machining properties.

FREDERICK C. LANGENBERG. 

